There is an ever increasing demand for fast, reliable and ad-hoc wireless data transfer between two or more terminal devices. Typical applications include mobile phones, laptop computers, cameras and printers. To satisfy such a demand, each of these devices should be equipped with a RF front-end module. In any case, miniaturization and low power consumption are the two most fundamental prerequisites for RF front-end modules.
One way to miniaturize a RF front-end module is to embed its passive circuitries, such as antenna, bandpass filter, balun, matching networks and interconnects, into a multi-layered substrate. Low Temperature Co-fired Ceramic technology (LTCC) is particularly suitable for this purpose since it can offer fine pitch lines and a multi-layered architecture for embedding passive circuits. FIG. 1 shows a block diagram for an example of such LTCC-based applications, namely, a Bluetooth system module 400. It is seen that two of the major embedded passives are the bandpass filter 410 and the balun 420.
Baluns, which converts a balanced signal to an unbalanced signal or vice versa, have been used in various RF circuitries such as those circuits interfacing with RFICs (Radio Frequency Integrated Circuits). Besides those traditionally known planar-type configurations, a number of multi-layered configurations have been proposed recently. These baluns, in general, are small and have good performance. However, they do not have specific transmission requirements over any frequency other than those within the operating frequency band. While prior art have analyzed some topologies that offer a bandpass-type of transmission response, information on how to shape up such response has never been addressed nor is the primary concern of them.
One of the fundamental representations of a balun is an ideal center-grounded transformer shown in FIG. 2. This transformer converts a single-ended input at an unbalanced terminal 510 to a differential output across a first balanced terminal 520 and a second balanced terminal 520, and vice versa, for all frequencies. In practice, however, such an ideal balun is hard to be realized due to the requirement of a high magnetic coupling.
In order to eliminate the need of two separate components for a balun and a bandpass filter in a typical integrated RF front-end module, a new device having both balun and bandpass filtering functions is provided in embodiments of the present invention.
The references cited herein are explicitly incorporated by reference in its entirety.